During the drilling, work over, or plug and abandonment of oil and gas producing wellbores, a variety of downhole tools may be attached to the lower portion or bottom hole assembly of a pipe or coiled tubing string. The attached tools are utilized to perform various functions within the wellbore and the bottom hole assembly may be provided with a variety of stabilizers, reamers, hole deviation devices, drill collars, and the like that enhance the wellbore characteristics such as its shape, geometry and direction.
It is often desirable to release the lower portion or bottom-bole of a pipe or coiled tubing pipe string from the upper portion when the lower portion is still in the wellbore. This occurs when a tool is inserted in the wellbore on the pipe string and released in order to provide some function after the pipe or coiled tubing string is removed. It also occurs when a tool or the BHA becomes stuck in the wellbore and the pipe or coiled tubing string must be removed from the wellbore, independent of the tool or BHA so that a fishing tool string may be placed in the wellbore in order to try to retrieve the stuck tool or BHA, The upper and lower portions of a pipe or coded tubing pipe string are typically released from each other by an intervening tool separation device that has detachable upper and lower sections or subs.
Some tool separation devices have mechanical separation mechanisms that employ shear pins or shear screws as a principal component of the release mechanism. Such separation devices have a number of shortcomings. The shear pins of these devices may prematurely separate when the pipe of coiled tubing string is in the wellbore causing the unintended release of the attached tool or BHA. A separated portion of a shear pin may also jam the release mechanism impeding or preventing, the release of the attached tool. There is also the risk that a shear pin or a separated portion of a shear pin will stray into and remain in a lower or bottom sub portion of the separation device after separation from the pipe or coiled tubing string. A separated shear pin in the bottom sub of a separation device may prevent or impede reengagement of the upper portion of the tool separation device with the bottom sub portion at a later time.
The majority of tool separation devices have hydraulic separation mechanisms which also have shortcomings. The hydraulic separation mechanisms of many of these tool separation devices often utilize a collet mechanism that is released by a piston or ball. The piston or ball of these mechanisms is often left in the lower or bottom sub portion of the separation device when the upper portion is released. A ball left in the bottom sub portion may prevent an operator from subsequently circulating fluid through the bottom sub. The hydraulic separation mechanisms of other such devices suffer from unreliable tool release mechanisms or require high pressures to release a tool from the pipe or coiled tubing string.
Consequently, there is a need for a new tool separation apparatus having improved piston and collet configurations that will reliably release a tool or BHA from a pipe or coiled tubing suing without the aforementioned negative attributes.